The purpose of studies to be conducted during this grant period is to characterize the effect of chronic intracellular infection with M. lepraemurium on the recirculation kinetics of thoracic duct lympocytes. Also, quantitation of theta-bearing lymphocyte populations in spleen, lymph node and thoracic duct lymph of normal and infected animals will be performed. The peripheral blood lymphocytes of humans with leprosy will be examined by a "sandwich" radio-immune labeling technique to determine if there is an abnormality in the proportion of thymus-dependent and Bursa-equivalent lymphocytes present.